South Sudan on Thursday accused the Khartoum government in the north of bombing 74 kilometers deep inside its territory, and of sending troops into contested border areas.

"They have flown into our territory 74 kilometers and are violating South Sudanese airspace," Information Minister Barnaba Marial Benjamin said of the airstrikes midday Wednesday.

U.S. Secretary of State Hillary Clinton on Wednesday accused Sudanese President Omar al-Bashir of trying to undermine newly independent South Sudan, adding Washington would consider increasing pressure on Bashir to reverse course.

Clinton told U.S. lawmakers that "what we've got with Bashir is a very determined effort to try to undo the results of the comprehensive peace agreement," which led to the creation last July of a separate state in South Sudan.

South Sudan has signed a ceasefire with the largest of several rebel groups which threaten the stability of the world's newest nation, the government said on Tuesday.

The deal to integrate an estimated 1,800 guerrilla fighters into the South's army comes after rebel chief and renegade general George Athor was killed by government forces in December.

Sudanese rebels said Tuesday they killed 150 government soldiers along the disputed border with South Sudan in a battle that prompted Khartoum to threaten retaliation against its newly independent neighbor.

Sudan's military denied the casualty toll and said it had killed a "huge number" of rebels, but gave no figure.

Two police officers from the African Union-United Nations peacekeeping mission to Sudan's Darfur region (UNAMID) have been shot and wounded by unidentified gunmen, the mission said on Saturday.

They both received leg wounds and were being treated at a UNAMID hospital, said Christopher Cycmanick, a spokesman for the mission.

United Nations international staff have returned to Sudan's South Kordofan for the first time in months, the U.N. said on Saturday, as global concern mounts over food shortages in the war-torn state.

"Today, FAO and OCHA flew back there by helicopter and they landed safely" in the state capital of Kadugli, Damian Rance, a public information officer at the UN Office for the Coordination of Humanitarian Affairs (OCHA), told AFP.

Sacked South Sudanese members of the Sudanese military pelted motorists and police with stones and blocked traffic on Wednesday to protest delays in their severance pay, witnesses said.

About 100 protesters gathered on Africa Road, a major artery in the Sudanese capital, shouting "We want our rights!"

Sudanese warplanes dropped several bombs wounding four soldiers in a contested area claimed by South Sudan, two days after agreeing to a non-aggression pact, Juba's military spokesman said Tuesday.

"Sudanese Armed Forces airplanes bombed the Jau area in Unity state on Sunday, wounding four of our soldiers," South Sudanese army spokesman Philip Aguer told Agence France Presse.

Two days of fresh fighting in Sudan's Blue Nile state have left "heavy losses" among rebel troops, the army said on Saturday, without giving casualty figures for either side.

The combat occurred west of Dindiro, some 100 kilometers southwest of the state capital of Ed Damazin, said Sudanese army spokesman Sawarmi Khaled Saad.

South Sudan must honor promises to investigate, arrest and prosecute those responsible for an explosion of bloody ethnic violence in war-wracked Jonglei state, Human Rights Watch said Friday.

"To stem this horrific cycle of violence, the organizers have to be held to account," said Daniel Bekele, HRW's Africa director, adding U.N. and African bodies should help for "speed and credibility’s sake."